A reinforced polyester resin composition is known as an engineering resin superior in various properties such as mechanical strength, stiffness, weather resistance, heat resistance, dimensional stability and chemical resistance and also is excellent in molding appearance, and is of extensively wide application for car use and industrial use.
In recent years, there has been a remarkable trend to replace car structural parts made of metal with those made of a reinforced thermoplastic resin, due to its reduced weight for the purpose of improving fuel expenses, cost saving and modular or integrated designing of parts. Such a resin material has been strongly desired to maintain its superior properties for a longer period of time even under more severe conditions. One of important performance characteristics particularly required for car exterior parts and materials for parts used near the engine is fatigue properties, and from the viewpoint of the designing parts, it becomes necessary that the resin material has improved fatigue properties.
As mentioned above, the resin material used for various structural members such as car parts has been further desired to be improved in long-term reliability of material properties.
Among reinforced polyester resins, a reinforced polytrimethylene terephthalate resin composition is particularly superior in mechanical properties, weather resistance, heat-aging resistance and molding appearance and therefore is expected to be developed for wide application.
However, with respect to dynamic mechanical properties such as fatigue properties, the reinforced polytrimethylene terephthalate resin has been examined to a lesser extent as compared with metal, and was deemed to be poor in long-term reliability of material properties under severe conditions such as when subjected to periodic stress. Furthermore, there has been almost no estimation of fatigue life of the reinforced polytrimethylene terephthalate material, and moreover there has been almost no quantitative analysis of the relationship between the fatigue properties and the polymer structure.
In the meantime, as a method for improving the fatigue properties, it has so far been generally accepted that glass fiber can be incorporated in a resin material in a high concentration to improve initial mechanical properties, thereby lengthening the fatigue life. However, the method is not always satisfactory, because problems result such as the weight of parts increasing and molding appearance becomes poor.
For example, JP-A-47-34444 discloses that a glass fiber-reinforced polytrimethylene terephthalate resin composition is blended with a third component, namely a polyfunctional compound, thereby improving mechanical properties and heat resistance. However, effects thereof are not yet sufficient. Moreover, due to the blending of the polyfunctional compound there is a problem such that flow properties at a low shear rate peculiar to the glass fiber-reinforced polytrimethylene terephthalte resin composition decrease and as a result poor appearance is observed at a flow terminal portion of a molded product.
Further, JP-A-53-106749 discloses that a glass fiber-reinforced polytrimethylene terephthalate resin composition is blended with glass fiber covered with a vinyl polymer, thereby improving mechanical strength and warping deformation. However, sufficient fatigue properties are not yet obtained.
Still further, JP-A-2001-172055 discloses a glass fiber-reinforced polybutylene terephthalate resin composition obtained by blending polybutylene terephthalate with a surface-treated glass fiber, which composition is described to be superior in mechanical strength, tracking resistance and hydrolysis resistance. However, the mechanical characteristics and fatigue characteristic exhibited are still too insufficient to be applied for structural parts.
An object of the present invention is to provide a reinforced polytrimethylene terephthalate resin composition, which has remarkable improvement in mechanical properties, particularly the fatigue characteristic without detriment to superior characteristics peculiar to the reinforced polytrimethylene terephthalate itself.